svrjs-blog-newsletter/cronjob/node_modules/smart-buffer/docs/README_v3.md

smart-buffer

smart-buffer is a light Buffer wrapper that takes away the need to keep track of what position to read and write data to and from the underlying Buffer. It also adds null terminating string operations and grows as you add more data.

What it's useful for:

I created smart-buffer because I wanted to simplify the process of using Buffer for building and reading network packets to send over a socket. Rather than having to keep track of which position I need to write a UInt16 to after adding a string of variable length, I simply don't have to.

Key Features:

• Proxies all of the Buffer write and read functions.
• Keeps track of read and write positions for you.
• Grows the internal Buffer as you add data to it.
• Useful string operations. (Null terminating strings)
• Allows for inserting values at specific points in the internal Buffer.
• Built in TypeScript
• Type Definitions Provided

Requirements:

• Node v4.0+ is supported at this time. (Versions prior to 2.0 will work on node 0.10)

Note:

smart-buffer can be used for writing to an underlying buffer as well as reading from it. It however does not function correctly if you're mixing both read and write operations with each other.

Breaking Changes with 2.0

The latest version (2.0+) is written in TypeScript, and are compiled to ES6 Javascript. This means the earliest Node.js it supports will be 4.x (in strict mode.) If you're using version 6 and above it will work without any issues. From an API standpoint, 2.0 is backwards compatible. The only difference is SmartBuffer is not exported directly as the root module.

Breaking Changes with 3.0

Starting with 3.0, if any of the readIntXXXX() methods are called and the requested data is larger than the bounds of the internally managed valid buffer data, an exception will now be thrown.

Installing:

npm install smart-buffer

or

yarn add smart-buffer

Note: The published NPM package includes the built javascript library. If you cloned this repo and wish to build the library manually use:

tsc -p ./

Using smart-buffer

Example

Say you were building a packet that had to conform to the following protocol:

[PacketType:2][PacketLength:2][Data:XX]

To build this packet using the vanilla Buffer class, you would have to count up the length of the data payload beforehand. You would also need to keep track of the current "cursor" position in your Buffer so you write everything in the right places. With smart-buffer you don't have to do either of those things.

// 1.x (javascript)
var SmartBuffer = require('smart-buffer');

// 1.x (typescript)
import SmartBuffer = require('smart-buffer');

// 2.x+ (javascript)
const SmartBuffer = require('smart-buffer').SmartBuffer;

// 2.x+ (typescript)
import { SmartBuffer, SmartBufferOptions} from 'smart-buffer';

function createLoginPacket(username, password, age, country) {
    let packet = new SmartBuffer();
    packet.writeUInt16LE(0x0060); // Login Packet Type/ID
    packet.writeStringNT(username);
    packet.writeStringNT(password);
    packet.writeUInt8(age);
    packet.writeStringNT(country);
    packet.writeUInt16LE(packet.length - 2, 2);
    
    return packet.toBuffer();
}

With the above function, you now can do this:

let login = createLoginPacket("Josh", "secret123", 22, "United States");

// <Buffer 60 00 1e 00 4a 6f 73 68 00 73 65 63 72 65 74 31 32 33 00 16 55 6e 69 74 65 64 20 53 74 61 74 65 73 00>

Notice that the [PacketLength:2] part of the packet was inserted after we had added everything else, and as shown in the Buffer dump above, is in the correct location along with everything else.

Reading back the packet we created above is just as easy:

let reader = SmartBuffer.fromBuffer(login);

let logininfo = {
    packetType: reader.readUInt16LE(),
    packetLength: reader.readUInt16LE(),
    username: reader.readStringNT(),
    password: reader.readStringNT(),
    age: reader.readUInt8(),
    country: reader.readStringNT()
};

/*
{ 
    packetType: 96, (0x0060)
    packetLength: 30,
    username: 'Josh',
    password: 'secret123',
    age: 22,
    country: 'United States' 
};
*/

Api Reference:

Constructing a smart-buffer

smart-buffer has a few different ways to construct an instance. Starting with version 2.0, the following factory methods are preffered.

let SmartBuffer = require('smart-buffer');

// Creating SmartBuffer from existing Buffer
let buff = SmartBuffer.fromBuffer(buffer); // Creates instance from buffer. (Uses default utf8 encoding)
let buff = SmartBuffer.fromBuffer(buffer, 'ascii'); // Creates instance from buffer with ascii encoding for Strings. 

// Creating SmartBuffer with specified internal Buffer size.
let buff = SmartBuffer.fromSize(1024); // Creates instance with internal Buffer size of 1024.
let buff = SmartBuffer.fromSize(1024, 'utf8'); // Creates instance with intenral Buffer size of 1024, and utf8 encoding. 

// Creating SmartBuffer with options object. This one specifies size and encoding.
let buff = SmartBuffer.fromOptions({
    size: 1024,
    encoding: 'ascii'
});

// Creating SmartBuffer with options object. This one specified an existing Buffer.
let buff = SmartBuffer.fromOptions({
    buff: buffer
});

// Just want a regular SmartBuffer with all default options?
let buff = new SmartBuffer();

Backwards Compatibility:

All constructors used prior to 2.0 still are supported. However it's not recommended to use these.

let writer = new SmartBuffer();               // Defaults to utf8, 4096 length internal Buffer.
let writer = new SmartBuffer(1024);           // Defaults to utf8, 1024 length internal Buffer.
let writer = new SmartBuffer('ascii');         // Sets to ascii encoding, 4096 length internal buffer.
let writer = new SmartBuffer(1024, 'ascii');  // Sets to ascii encoding, 1024 length internal buffer.

Reading Data

smart-buffer supports all of the common read functions you will find in the vanilla Buffer class. The only difference is, you do not need to specify which location to start reading from. This is possible because as you read data out of a smart-buffer, it automatically progresses an internal read offset/position to know where to pick up from on the next read.

Reading Numeric Values

When numeric values, you simply need to call the function you want, and the data is returned.

Supported Operations:

• readInt8
• readInt16BE
• readInt16LE
• readInt32BE
• readInt32LE
• readBigInt64LE
• readBigInt64BE
• readUInt8
• readUInt16BE
• readUInt16LE
• readUInt32BE
• readUInt32LE
• readBigUInt64LE
• readBigUInt64BE
• readFloatBE
• readFloatLE
• readDoubleBE
• readDoubleLE

let reader = new SmartBuffer(somebuffer);
let num = reader.readInt8();

Reading String Values

When reading String values, you can either choose to read a null terminated string, or a string of a specified length.

SmartBuffer.readStringNT( [encoding] )

String String encoding to use - Defaults to the encoding set in the constructor.

returns String

Note: When readStringNT is called and there is no null character found, smart-buffer will read to the end of the internal Buffer.

SmartBuffer.readString( [length] )

SmartBuffer.readString( [encoding] )

SmartBuffer.readString( [length], [encoding] )

Number Length of the string to read

String String encoding to use - Defaults to the encoding set in the constructor, or utf8.

returns String

Note: When readString is called without a specified length, smart-buffer will read to the end of the internal Buffer.

Reading Buffer Values

SmartBuffer.readBuffer( length )

Number Length of data to read into a Buffer

returns Buffer

Note: This function uses slice to retrieve the Buffer.

SmartBuffer.readBufferNT()

returns Buffer

Note: This reads the next sequence of bytes in the buffer until a null (0x00) value is found. (Null terminated buffer) Note: This function uses slice to retrieve the Buffer.

Writing Data

smart-buffer supports all of the common write functions you will find in the vanilla Buffer class. The only difference is, you do not need to specify which location to write to in your Buffer by default. You do however have the option of inserting a piece of data into your smart-buffer at a given location.

Writing Numeric Values

For numeric values, you simply need to call the function you want, and the data is written at the end of the internal Buffer's current write position. You can specify a offset/position to insert the given value at, but keep in mind this does not override data at the given position. This feature also does not work properly when inserting a value beyond the current internal length of the smart-buffer (length being the .length property of the smart-buffer instance you're writing to)

Supported Operations:

• writeInt8
• writeInt16BE
• writeInt16LE
• writeInt32BE
• writeInt32LE
• writeBigInt64BE
• writeBigInt64LE
• writeUInt8
• writeUInt16BE
• writeUInt16LE
• writeUInt32BE
• writeUInt32LE
• writeBigUInt64BE
• writeBigUInt64LE
• writeFloatBE
• writeFloatLE
• writeDoubleBE
• writeDoubleLE

The following signature is the same for all the above functions:

SmartBuffer.writeInt8( value, [offset] )

Number A valid Int8 number

Number The position to insert this value at

returns this

Note: All write operations return this to allow for chaining.

Writing String Values

When reading String values, you can either choose to write a null terminated string, or a non null terminated string.

SmartBuffer.writeStringNT( value, [offset], [encoding] )

SmartBuffer.writeStringNT( value, [offset] )

SmartBuffer.writeStringNT( value, [encoding] )

String String value to write

Number The position to insert this String at

String The String encoding to use. - Defaults to the encoding set in the constructor, or utf8.

returns this

SmartBuffer.writeString( value, [offset], [encoding] )

SmartBuffer.writeString( value, [offset] )

SmartBuffer.writeString( value, [encoding] )

String String value to write

Number The position to insert this String at

String The String encoding to use - Defaults to the encoding set in the constructor, or utf8.

returns this

Writing Buffer Values

SmartBuffer.writeBuffer( value, [offset] )

Buffer Buffer value to write

Number The position to insert this Buffer's content at

returns this

SmartBuffer.writeBufferNT( value, [offset] )

Buffer Buffer value to write

Number The position to insert this Buffer's content at

returns this

Utility Functions

SmartBuffer.clear()

Resets the SmartBuffer to its default state where it can be reused for reading or writing.

SmartBuffer.remaining()

returns Number The amount of data left to read based on the current read Position.

SmartBuffer.skip( value )

Number The amount of bytes to skip ahead

Skips the read position ahead by the given value.

returns this

SmartBuffer.rewind( value )

Number The amount of bytes to reward backwards

Rewinds the read position backwards by the given value.

returns this

SmartBuffer.moveTo( position )

Number The point to skip the read position to

Moves the read position to the given point. returns this

SmartBuffer.toBuffer()

returns Buffer A Buffer containing the contents of the internal Buffer.

Note: This uses the slice function.

SmartBuffer.toString( [encoding] )

String The String encoding to use - Defaults to the encoding set in the constructor, or utf8.

returns String The internal Buffer in String representation.

Properties

SmartBuffer.length

returns Number The length of the data that is being tracked in the internal Buffer - Does NOT return the absolute length of the internal Buffer being written to.

License

This work is licensed under the MIT license.